Provided by: libpmemobj-dev_1.13.1-1.1ubuntu2_amd64 
NAME
pmemobj_persist(), pmemobj_xpersist(), pmemobj_flush(), pmemobj_xflush(), pmemobj_drain(), pmemobj_mem‐
cpy(), pmemobj_memmove(), pmemobj_memset(), pmemobj_memcpy_persist(), pmemobj_memset_persist() - low-lev‐
el memory manipulation functions
SYNOPSIS
#include <libpmemobj.h>
void pmemobj_persist(PMEMobjpool *pop, const void *addr,
size_t len);
void pmemobj_flush(PMEMobjpool *pop, const void *addr,
size_t len);
void pmemobj_drain(PMEMobjpool *pop);
int pmemobj_xpersist(PMEMobjpool *pop, const void *addr,
size_t len, unsigned flags);
int pmemobj_xflush(PMEMobjpool *pop, const void *addr,
size_t len, unsigned flags);
void *pmemobj_memcpy(PMEMobjpool *pop, void *dest,
const void *src, size_t len, unsigned flags);
void *pmemobj_memmove(PMEMobjpool *pop, void *dest,
const void *src, size_t len, unsigned flags);
void *pmemobj_memset(PMEMobjpool *pop, void *dest,
int c, size_t len, unsigned flags);
void *pmemobj_memcpy_persist(PMEMobjpool *pop, void *dest,
const void *src, size_t len);
void *pmemobj_memset_persist(PMEMobjpool *pop, void *dest,
int c, size_t len);
DESCRIPTION
The libpmemobj-specific low-level memory manipulation functions described here leverage the knowledge of
the additional configuration options available for libpmemobj(7) pools, such as replication. They also
take advantage of the type of storage behind the pool and use appropriate flush/drain functions. It is
advised to use these functions in conjunction with libpmemobj(7) objects rather than using low-level mem‐
ory manipulation functions from libpmem.
pmemobj_persist() forces any changes in the range [addr, addr+len) to be stored durably in persistent
memory. Internally this may call either pmem_msync(3) or pmem_persist(3). There are no alignment re‐
strictions on the range described by addr and len, but pmemobj_persist() may expand the range as neces‐
sary to meet platform alignment requirements.
WARNING: Like msync(2), there is nothing atomic or transactional about this call. Any unwritten
stores in the given range will be written, but some stores may have already been written by virtue
of normal cache eviction/replacement policies. Correctly written code must not depend on stores
waiting until pmemobj_persist() is called to become persistent - they can become persistent at any
time before pmemobj_persist() is called.
The pmemobj_flush() and pmemobj_drain() functions provide partial versions of the pmemobj_persist() func‐
tion described above. These functions allow advanced programs to create their own variations of pmemo‐
bj_persist(). For example, a program that needs to flush several discontiguous ranges can call pmemo‐
bj_flush() for each range and then follow up by calling pmemobj_drain() once. For more information on
partial flushing operations, see pmem_flush(3).
pmemobj_xpersist() is a version of pmemobj_persist() function with additional flags argument. It sup‐
ports only the PMEMOBJ_F_RELAXED flag. This flag indicates that memory transfer operation does not re‐
quire 8-byte atomicity guarantees.
pmemobj_xflush() is a version of pmemobj_flush() function with additional flags argument. It supports
only the PMEMOBJ_F_RELAXED flag.
The pmemobj_memmove(), pmemobj_memcpy() and pmemobj_memset() functions provide the same memory copying as
their namesakes memmove(3), memcpy(3), and memset(3), and ensure that the result has been flushed to per‐
sistence before returning (unless PMEMOBJ_MEM_NOFLUSH flag was used). Valid flags for those functions:
• PMEMOBJ_F_RELAXED - This flag indicates that memory transfer operation does not require 8-byte atomici‐
ty guarantees.
• PMEMOBJ_F_MEM_NOFLUSH - Don’t flush anything. This implies PMEMOBJ_F_MEM_NODRAIN. Using this flag on‐
ly makes sense when it’s followed by any function that flushes data.
The remaining flags say how the operation should be done, and are merely hints.
• PMEMOBJ_F_MEM_NONTEMPORAL - Use non-temporal instructions. This flag is mutually exclusive with PMEMO‐
BJ_F_MEM_TEMPORAL. On x86_64 this flag is mutually exclusive with PMEMOBJ_F_MEM_NOFLUSH.
• PMEMOBJ_F_MEM_TEMPORAL - Use temporal instructions. This flag is mutually exclusive with PMEMO‐
BJ_F_MEM_NONTEMPORAL.
• PMEMOBJ_F_MEM_WC - Use write combining mode. This flag is mutually exclusive with PMEMOBJ_F_MEM_WB.
On x86_64 this is an alias for PMEMOBJ_F_MEM_NONTEMPORAL. On x86_64 this flag is mutually exclusive
with PMEMOBJ_F_MEM_NOFLUSH.
• PMEMOBJ_F_MEM_WB - Use write back mode. This flag is mutually exclusive with PMEMOBJ_F_MEM_WC. On
x86_64 this is an alias for PMEMOBJ_F_MEM_TEMPORAL.
pmemobj_memcpy_persist() is an alias for pmemobj_memcpy() with flags equal to 0.
pmemobj_memset_persist() is an alias for pmemobj_memset() with flags equal to 0.
RETURN VALUE
pmemobj_memmove(), pmemobj_memcpy(), pmemobj_memset(), pmemobj_memcpy_persist() and pmemobj_memset_per‐
sist() return destination buffer.
pmemobj_persist(), pmemobj_flush() and pmemobj_drain() do not return any value.
pmemobj_xpersist() and pmemobj_xflush() returns non-zero value and sets errno to EINVAL only if not sup‐
ported flags has been provided.
EXAMPLES
The following code is functionally equivalent to pmemobj_memcpy_persist():
void *
pmemobj_memcpy_persist(PMEMobjpool *pop, void *dest,
const void *src, size_t len)
{
void *retval = memcpy(dest, src, len);
pmemobj_persist(pop, dest, len);
return retval;
}
pmemobj_persist() can be thought of as this:
void
pmemobj_persist(PMEMobjpool *pop, const void *addr, size_t len)
{
/* flush the processor caches */
pmemobj_flush(pop, addr, len);
/* wait for any pmem stores to drain from HW buffers */
pmemobj_drain(pop);
}
SEE ALSO
memcpy(3), memset(3), pmem_msync(3), pmem_persist(3), libpmem(7) libpmemobj(7) and <https://pmem.io>